Electric fuse



(No Model.)

G. F. GURTISS.

ELECTRIC FUSE.

No. 449,209. Patented Mar.31,1891.

WITNESSES: l/VVE/VTOI? UNITED STATES PATENT OFFICE.

GEORGE F. OURTISS, OF LYNN, MASSACHUSETTS, ASSIGNOR- TO THE THOMSON- HOUSTON ELECTRIC COMPANY, OF CONNECTICUT.

ELECTRIC FUSE.

SPECIFICATION forming part of Letters Patent No. 449,209, dated March 81 1891.

Application, filed June 20, 1890. Serial No. 356,148. (No model.)

T0 at whom it may concern:

Be it known that I, GEORGE l OURTISS, av citizen of the United States, residing at Lynn, county of Essex, and State of Massachusetts, have invented certain new and useful Improvements in Electric Fuses, of which the following is a specification.

My present invention relates to fuses for electric circuits.

The invention consists in certain novel features in the construction of the fuse, whereby it may be readily inserted into the circuit to be protected, and whereby new properties are conferred on the fuse, by which the length of fuse-wire required to protect a circuit of a given potential is very considerably reduced, and the efficiency of the fuse in rupturing the circuit is greatly enhanced.

The specific form of apparatus given as illustrative of the invention consists in f usewire surrounded by a retaining-tube of insulating material, preferably of glass orearthenware. The diameter of the tubeis such that the fuse-wire substantially fills the tube, and the ends of the fuse-wire are secured to conducting-collars placed about the ends of the tube, where they will not obstruct the passage of any gas or vapor expelled explosively therefrom.

In carrying the invention into practice the fuse-wire, which may be any electrical conductor having a low melting temperature as compared with the conductor of the circuit in which it is placed, is inserted into a tube of insulating material, and at the ends of the wire are provided terminals for making electrical connection with the circuit to be protected.

I have found by a series of experiments that the relation between the diameters of the fuse-wire and the bore of the tube in which it is inserted is of the utmost importance. If the bore of the tube be considerably greater than the diameter of the wire-say more than twenty or twenty-five per cent.the tube will be shattered into fragments when the wire is melted by an abnormal current, because the gas formed from the metal, being unconfined, finds ready egress from the ends of the tube, the fuse-wire retains its position in the tube,

and the are plays between the ruptured ends until all of the wire is volatilized. If, however, the bore of the tube be made small, so that the fuse-wire fills it with slight, if any,

clearance, the gas first formed is confined,

and to relieve the pressure the wire is blown bodily out of the tube, thus quickly rupturing the circuit, while the are produced is so instantly disrupted that the tube, al-

though made of brittle material, such as glass, remains practically intact. Moreover, the tube surrounding the fuse-wire exerts acooling tendency on the volatilized or gaseous metal, tending to condense it, and this also assists in breaking the are by reduc- The action,indeed,is so instantaneous that there is not time for the force of the explosion to be communicated to the surrounding envelope, and in the numerous experiments made there was found no instance in which the tube was fractured if the proper relation So between the diameter of the fuse-wire and bore of the tube was preserved. On the other hand, when the bore of the tube was made relatively large in diameter, as compared with the diameter of the fuse-wire, the tube was uniformly broken and in most instances shattered into fragments.

The accompanying figures will illustrate my invention, wherein- Figure 1 is a part section and part side view 0 of a fuse embodying the principles of my invention. Figs. 2, 3, 4i, and 5 illustrate the means for holding the fuse-wire in place. Fig. 6 illustrates the action of a fuse thus constructed. Fig. 7 shows circuit-including 5 clips for holding the fuse in place. Fig. 8 illustrates a fuse as made similar in appear ance to that of Fig. l, but improperly proportioned, and with which the results ob tained with the fuse of Fig. 1 cannot be had. I00

In Fig. 1, G is a tube of glass, earthenware, or other insulating material, the bore of which, as shown,is just large enough to admit of the entrance of the fuse-wire F with very little clearance. For example, the bore of the tube should not be more than twenty to twentyfive per cent. larger than the diameter of the wire itself. The ends of the-wire Fare bent back and clamped in retaining-collars C C, secured about the ends of the tube. These clips may be made by bending a strip of copper into the shape shown in Fig. 2 and then soldering the ends together and to the fuse-wire, as at E; but a preferred mode of constructing them is to take a copper tube having a diametera's much larger than the insulatingtube (see Fig. 4-) as will, when pressed into position, leave aspace bet-ween the tube and collar for the reception of the fuse-wire, as-illustrated at H, Fig. 5. The ends of the wire F are inserted intothis space H and carefully soldered to make intimate contact,

In Fig. 6 there is illustrated the'action of afuse-so constructed when it melts-in an.

electric circuit. Thepoint of fusion is nearly always at the central portion of the fuse-wire, and themetallic gases formed forcibly expel the w-irefrom the tube at one or both ends,

rupturing the circuit. This action occurs so instantaneously that the heat ofthe arc has not timeto communicate itself to the tube to break it, and the violent expulsion of the fuse-wire makes i t possible to employ a much shorter length of wire than would otherwise be necessary. If, however, the diameter of the wire is considerably less than the bore of the tube, as in Fig. 8, the gases formed when the wire melts can readily escape alongthe sides. The fuse remains in position and maintains the arc, whereby the heat produced cracks the tube, the arc oftentimes continuing, between the terminals, unless they are situated at a much greater distance apart than would be used with a fuse constructed as shown in Fig. 1.

K, Fig. 7, are metalclips made to hold and make electrical contact with the metallic collars on the end of the fuse, which can of course be constructed in a variety of ways.

What I claim as new, and desire to secure by Letters Patent, is-

1. In an electric fuse, the combination of the fuse-wire with an inclosing tube having a bore of such diameter that the wire fills the tube with slight, if any, clearance for the purpose of causing the sudden expulsion of the wire when melted, as described.

2. In an electric fuse, the combination of the fuse-wire with an inclosing tubeof insulating material having a bore of such diameter that the wire fills the tube with slight, if any, clearance, and terminals exterior to the tube for making connection with the electric circuit to be protected.

3. The combination, in an electric fuse, of the inclosing tube and a fusible conductor of such diameter as will fill the tube with slight, if any, clearance bent back at its ends, with metallic collars external to the tube, with which the-ends of the conductor are in electrical connection, as described.

4. The combination, with the inclosing tube, of a fuse-wire therein bent back at its ends, and the metallic collars G 0 around the ends of the tube, shaped. to leave spaces between the collar and tube, into which are inserted the ends of the fuse-wire, as described.

Signedat'Lynn, Massachusetts,- June 16,

GEORGE F. OURTISS.

Witnesses:

JOHN W.-G1sBoNEY, ALBERT L. Bounce.- 

